A device and a method of this type are known from WO 02/060264 A1.
Furthermore, extrusion systems are known with which several skinless strands of sausage meat are produced and processed at the same time. These extrusion systems comprise a plurality of extrusion nozzles that are horizontally arranged side by side, and they are capable of producing up to ten strands running in parallel with one another from the machine. A reservoir is here provided, from which sausage meat is pumped through a feed line into a distributor which supplies the sausage meat to the individual nozzles. The distributor is configured as a pressure chamber which is followed by a pump block which conveys the sausage meat contained in the pressure chamber to the nozzles. Air inclusions are avoided by conveying the sausage meat into the pressure chamber, and homogenization is achieved. Moreover, a compensating buffer effect is achieved between the supply and the pump delivery.
Such systems, however, are only configured for extruding skinless strands. The coextrusion of sausages which are surrounded with a skin poses special problems that do not arise during extrusion, especially as regards the mounting of the sausage casing.
An example of a coextrusion system in which a collagen casing is injected around a pasty inner mass, especially consisting of sausage meat, is known from EP 1 371 293. This coextrusion system is equipped with a single coextrusion head. The material for producing the casing is supplied by means of a pump to the coextrusion head and is injected, by means of an annular gap which coaxially surrounds the inner mass in the coextrusion head, onto said mass, whereby an outer skin is produced.
Although the percentage of the outer skin in the whole sausage is only small, variations in the delivered amount of the casing material have a strongly disadvantageous effect because a supply amount varying from product to product must not be fallen below for producing a stable, i.e. sufficiently thick, sausage casing. On the other hand, however, the amount of the supplied casing material should not be too great. Although a great amount improves the stability of the sausage casing, the further treatment of the products is impaired because the drying time is in particular extended. Furthermore, a sausage casing that is too thick has a disadvantageous effect on the later consumption of the product because in such a case the sausage is not “crispy”.
The stability of the sausage casing on the one hand and the fast further treatment of the product and the consumption friendliness on the other hand can only be ensured if very narrow quantitative tolerances are observed during supply of the casing material.
The quantitatively exact supply of casing material is further rendered difficult if several parallel-operating coextrusion heads are used for simultaneously producing several sausage strands.
Such a coextrusion system with several heads is known from the above-mentioned WO 02/060264 A1. This system comprises six coextrusion heads that are arranged in parallel and are connected to a distributor strip for the supply of sausage meat and to a distributor strip for the supply of casing material. Each of the distributor strips are coupled via individual lines to the various coextrusion heads and are fed via two feed lines with sausage meat and casing material, respectively. The sausage meat and the casing material are divided in the respective feed line and are then supplied via the individual lines to the parallel-arranged coextrusion heads. This entails great pressure differences in the individual lines, which has an extremely negative effect on the supply of the casing material because it is thus not possible to produce uniformly thick outer skins of a reproducible quality. Moreover, the skin thickness cannot be adapted to different products.
That is why efforts were taken to produce products of uniform preciseness with a sufficiently constant skin thickness on coextrusion systems comprising several coextrusion heads.
To this end the joint supply of the filling material and of the casing material, respectively, was above all abandoned and replaced by individually supplied coextrusion heads so that each coextrusion head has assigned to it at least one pump of its own for the supply of mass material. Although this achieves a certain influence on the supply amount via the delivery rate of the respective pump, the power consumption of the coextrusion system is considerably increased by the use of several pumps. Moreover, this concept does not permit a fast and flexible adaptation to short-term quantitative variations because such a system normally reacts with too much inertia.
The above-cited WO 02/060264 A1 further discloses that the output rate of the individual coextrusion heads should be adjusted. This is important insofar as in the further processing process the individual sausage strands are combined to form bunches, which is facilitated by a homogeneous output rate. The problem regarding the production of stable sausage casings that are not too thick at the same time is not touched thereby.